Cases20 cases

6 to 10 of 20

1. IL-0226 Azure Front Door edge servers crashed worldwide on incompatible configuration metadata, causing timeouts and DNS errors

   Microsoft Azure2025

   Symptoms

   From 15:41 UTC on 29 October 2025, customers and Microsoft services using Azure Front Door (AFD) and Azure Content Delivery Network (CDN) got connection timeout errors and DNS resolution issues. Monitoring alerts started the investigation at 15:48 UTC.

   Intermittent timeoutsDNS resolution failuresService outageHigh latency

   Trigger

   At 15:35 UTC a specific sequence of valid customer configuration changes, made across two different AFD control plane build versions, produced incompatible customer configuration metadata that was deployed to the edge sites.

   Root cause

   Software defect

   Component

   CDN and edge networkAuthoritative DNS servers and records

   Contributing factor

   Gap in automated testsChange with a delayed effectIneffective rollbackExcessive blast radius

   Detection

   The configuration protection system detected the data plane impact and blocked configuration changes at 15:43 UTC, and monitoring alerts started the investigation at 15:48 UTC.

   Remediation

   • The configuration protection system automatically blocked all new and in-flight configuration changes worldwide
   • Removed the problematic customer configurations from the latest LKG snapshot by hand
   • Blocked all customer configuration changes from propagating to the data plane
   • Deployed the updated LKG configuration across the global fleet
   • Moved Azure Portal away from Azure Front Door
   • Rebalanced traffic by hand to a few healthy edge sites, then switched back to automatic traffic management
   • Blocked all AFD customer configuration changes at the Azure Resource Manager level until safeguards were in place

   Action items

   • Fix the control plane incompatibility and the data plane bug
   • Process each customer configuration completely and synchronously before production stages
   • Add stages to the phased configuration rollout, with longer bake time between them
   • Move configuration processing on data plane servers into isolated worker processes
   • Reduce configuration propagation time from 45 minutes to about 15 minutes
   • Test backwards compatibility with configurations generated by earlier control plane builds
   • Move critical first-party infrastructure to an active-active setup with fail away
   • Isolate customer configuration and traffic with micro cell segmentation of the AFD data plane
   • Restore customer configurations within one hour by using the local configuration cache
   • Cut data plane recovery further, to about 10 minutes
   • Remove delays in Azure Service Health alerts by raising resource thresholds
   • Extend automated Azure Service Health alerts to similar classes of service degradation
   • Fail over support request systems faster so Premier and Unified customers can always open requests

   Lessons

   Microsoft describes configuration propagation risk as inherent to a global Content Delivery Network, in which route, WAF and origin changes must be deployed quickly worldwide. Both this incident and the 9 October AFD incident came from that risk. This time the incompatible metadata passed a protection system that advances only on healthy data plane signals, because the crash came later from delayed asynchronous processing. Some learnings and repair items from the earlier incident applied here as well. Microsoft advises customers to build a resilient global HTTP ingress layer that stays available during regional or network disruptions, to manage resources through the REST API or PowerShell when management portals are unavailable, and to configure Azure Service Health alerts so the right people hear about service issues.

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2. IL-0357 Up to 22% of Vercel static file requests failed when part of its global cache was lost during the AWS us-east-1 outage

   Vercel2025

   Symptoms

   On 20 October 2025 at 07:45 UTC, while Vercel was moving traffic away from its us-east-1 region (iad1) during the AWS us-east-1 outage, a cascading failure took out a percentage of Vercel's global caching infrastructure. Failures of static file serving peaked at about 22% of traffic, the largest impact of the whole event, until service was restored at 08:18 UTC.

   High error rate

   Trigger

   The AWS us-east-1 region (Vercel's iad1) failed on 20 October 2025, and Vercel began re-routing traffic and function invocations away from it; at 07:45 UTC a cascading failure followed in the global caching infrastructure.

   Root cause

   Cloud provider outage

   Component

   CDN and edge networkObject storage

   Contributing factor

   –

   Detection

   The first automated alerts, for errors across Vercel services, fired at 06:55 UTC at the start of the us-east-1 disruption, 50 minutes before the cache failure began; incidents were created automatically and on-call engineers were paged.

   Remediation

   • Re-routed end-user traffic away from iad1 into neighbouring data centers
   • Re-routed function invocations to configured backup or secondary regions
   • Restored static file serving at 08:18 UTC and mitigated the root cause of the cascading cache failure

   Action items

   • Write a detailed technical postmortem leading to systematic mitigation of the failure modes these disruptions exposed
   • Continue and intensify rehearsals of major regional disruptions

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3. IL-0341 Traffic between Cloudflare and AWS us-east-1 had high latency, packet loss and origin failures for almost four hours

   Cloudflare2025

   Symptoms

   From 16:27 UTC on 21 August 2025, users connecting to Cloudflare from servers in AWS us-east-1, or receiving connections from Cloudflare there, saw high latency, packet loss and failures to reach origins. Cloudflare's network team was alerted to internal congestion in Ashburn (IAD) at 16:44 UTC.

   Packet lossHigh latencyIntermittent timeouts

   Trigger

   At about 16:27 UTC a single customer began sending many requests from AWS us-east-1 to Cloudflare for objects in Cloudflare's cache, doubling the total traffic from Cloudflare to AWS.

   Root cause

   Capacity exhaustion

   Component

   Transit gateway or network interconnectBGP routingCDN and edge network

   Contributing factor

   No headroomHarmful manual actionExcessive blast radius

   Detection

   Cloudflare's network team was alerted to internal congestion in Ashburn (IAD) at 16:44 UTC, and an incident was raised for customer impact at 17:45 UTC.

   Remediation

   • Rate limited the single customer whose traffic caused the surge
   • Took further traffic engineering actions that fully resolved the congestion
   • Asked AWS to revert its BGP prefix withdrawals, which AWS finished at 20:07 UTC

   Action items

   • Build a mechanism to deprioritise a customer's traffic when it congests the network enough to affect others
   • Speed up the Data Center Interconnect upgrades to add network capacity
   • Work with AWS so the two companies' BGP traffic engineering actions do not conflict
   • Build a traffic management system that gives each customer a network resource budget and automates the manual actions used here

   Lessons

   Cloudflare concludes that it must isolate customers better so that no single customer can take over shared network resources and degrade the platform for others, and that its network needs enough capacity to meet demand. It describes the outage as the result of insufficient network congestion management during an unusual high-traffic event.

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4. IL-0584 Cloud CDN at Osaka served corrupted JavaScript files, and a single-page app failed with a SyntaxError in western Japan

   Monicle2024

   Symptoms

   Some users reported that a Monicle web service could not be used. The service is a single-page app (SPA) served through Google Cloud Load Balancing and Cloud CDN, and in the affected browsers the app stopped with a SyntaxError. Users in eastern Japan were not affected; users in western Japan were.

   Response quality degradation

   Root cause

   Cloud provider outage

   Component

   CDN and edge network

   Contributing factor

   –

   Detection

   Some users reported that they could not use the system, and a war room was opened right away because of the product and the extent of the impact.

   Remediation

   • Purged the Cloud CDN cache after the corruption was seen at KIX (Osaka) but not at NRT (Tokyo)
   • Enabled compression_mode for Cloud CDN content on Cloud Load Balancing, after which the app worked for users again

   Action items

   • Stay aware of which parts of the service are single points of failure, remove them where the cost is justified, and prepare to respond quickly to failures in PaaS and SaaS products

   Lessons

   The author states that there is no specific countermeasure for this incident yet. The lesson drawn is to keep in mind which parts of the service are single points of failure and to be ready to act quickly on failures in PaaS and SaaS products.

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5. IL-0257 canva.com went down for about 50 minutes when 1.5 million requests per second OOM-killed every API Gateway task

   Canva2024

   Symptoms

   On 12 November 2024, after a new version of Canva's editor was deployed at 8:47 AM UTC, the editor's object panel stayed in a perpetual loading state for many users, particularly in Asia. Then from 9:08 AM UTC to about 10:00 AM UTC canva.com was unavailable and all requests to it failed.

   Service outageOOMKilledHigh latencyPacket loss

   Trigger

   At 8:47 AM UTC a new version of the Canva editor page was deployed, and client devices began fetching its new static assets through Cloudflare while the network path between Cloudflare's Singapore and Ashburn locations was losing packets.

   Root cause

   Dependency failure

   Component

   CDN and edge networkAPI gatewayAmazon ECS

   Contributing factor

   Overlapping failuresMonitoring blind spotRetry stormAutomation amplificationUnpatched known bug

   Remediation

   • Added a temporary Cloudflare firewall rule at 9:29 AM UTC that blocked all traffic at the CDN so new API Gateway tasks could start
   • Redirected canva.com to the status page
   • Restored traffic gradually, starting with Australian users under strict rate limits

   Action items

   • Write a runbook for rerouting, blocking and progressively restoring traffic
   • Show users a more informative error page when canva.com is unavailable
   • Raise the baseline number of API Gateway tasks and the memory of each task
   • Add load shedding rules to the API Gateway for similar traffic patterns
   • Load test the API Gateway regularly
   • Deploy the patch for the thread-locking bug in the telemetry library
   • Add multithreaded tests for the contended code path to the telemetry library microbenchmark suite
   • Use page load completion events as a second canary indicator for page asset releases
   • Experiment with adding another rollout stage to the canary to give more time to detect issues
   • Add timeouts so user requests do not wait excessively long for assets
   • Work with Cloudflare to understand the system interactions behind the incident

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